First the picture most be uploaded and hosted online somewhere. Such as Picassa, Photobucket, etc. You will need to copy the address or cut and paste the address of the uploaded photo into the message.

If you want the photo to display automatically, as below, then you will need to add the "img" tags to the front and back of the address of the photo, including the square brackets, it will look like the following (less the space in the first img):

[IM G]http://benchrest.ca/uploads/IMG_5766.JPG[/img]

L-R Joe M., Rob S., Tony G.

You can also just paste the hotlink in the message and people can click on it to see the photo. Just as below.